Voltage compensator for dual-secondary voltage transformers

Abstract

An compensated voltage transformer includes a voltage transformer. The voltage transformer includes a primary winding that receives a supply voltage, a meter winding that generates a first voltage based on a first turns ratio between the primary winding and the meter winding, and a power winding that generates a second voltage based on a second turns ratio of the primary winding to the power winding. A current transformer includes a primary winding and a secondary winding. The primary winding carries a load current that flows through the power winding and the secondary winding connects to the meter winding.

1 . A compensated voltage transformer, comprising:
 a voltage transformer that includes
 a primary winding that receives a supply voltage, 
 a meter winding that generates a first voltage based on a first turns ratio between the primary winding and the meter winding, and 
 a power winding that generates a second voltage based on a second turns ratio of the primary winding to the power winding; and 
   a current transformer that includes a primary winding and a secondary winding, wherein the primary winding carries a load current that flows through the power winding and the secondary winding connects to the meter winding.   
   
   
       2 . The compensated voltage transformer of  claim 1  further comprising a compensation impedance connected across the secondary winding, wherein the compensation impedance generates a compensation voltage that is summed with a meter voltage which is generated by the meter winding. 
   
   
       3 . The compensated voltage transformer of  claim 2  wherein the compensation impedance comprises a resistance and a reactance. 
   
   
       4 . The compensated voltage transformer of  claim 3  wherein the resistance and the reactance are connected in series. 
   
   
       5 . The compensated voltage transformer of  claim 2  wherein the compensation voltage is proportional to a voltage that is dropped by an impedance of the primary winding. 
   
   
       6 . The compensated voltage transformer of  claim 5  wherein the compensation voltage is equal to the voltage dropped by the impedance of the primary winding divided by a turns ratio of the primary winding to the meter winding. 
   
   
       7 . A compensated voltage transformer, comprising:
 a voltage transformer that includes
 a primary winding that receives a supply voltage, 
 a meter winding that generates a first voltage based on a first turns ratio between the primary winding and the meter winding, and 
 a power winding that generates a second voltage based on a second turns ratio of the primary winding to the power winding; 
   a current transformer that includes a primary winding that connects to the power winding and a secondary winding that connects to the meter winding; and   a compensation impedance connected across the secondary winding, wherein the compensation impedance generates a voltage that is summed with the first voltage to provide a metering voltage.   
   
   
       8 . The compensated voltage transformer of  claim 7  wherein the compensation impedance comprises a resistance and a reactance. 
   
   
       9 . The compensated voltage transformer of  claim 8  wherein the resistance and the reactance are connected in series. 
   
   
       10 . The compensated voltage transformer of  claim 7  wherein the meter winding and the power winding have unequal numbers of turns. 
   
   
       11 . A method of compensating a secondary voltage in a multi-secondary voltage transformer, comprising:
 applying a supply voltage to a primary winding of a voltage transformer;   providing a load current to a load from a first secondary winding of the voltage transformer;   generating a first voltage across a second secondary winding of the voltage transformer;   transforming the load current to a second current;   generating a second voltage based on the second current; and   summing the first voltage and the second voltage to generate a meter voltage that is based on the supply voltage and the load current.   
   
   
       12 . The method of  claim 11  wherein generating the second voltage includes passing the second current through an impedance. 
   
   
       13 . A compensation circuit for a multi-secondary voltage transformer, comprising:
 a current transformer including
 a primary winding for connecting to a first secondary winding of a multi-secondary voltage transformer; and 
 a secondary winding for connecting to second secondary winding of the multi-secondary voltage transformer; and 
   an impedance that conducts current of the current transformer secondary winding and thereby drops a compensation voltage, wherein the compensation voltage is proportional to a voltage drop of a primary winding of the multi-secondary voltage transformer.   
   
   
       14 . The compensation circuit of  claim 13  wherein the current transformer primary winding conducts a load current of the multi-secondary voltage transformer. 
   
   
       15 . The compensation circuit of  claim 13  wherein the compensation impedance comprises a resistance and a reactance. 
   
   
       16 . The compensation circuit of  claim 15  wherein the compensation impedance comprises a resistor and an inductor.